Degassing method, degassing device and use of screw elements

ABSTRACT

The present invention relates to a process for devolatilizing polymer-containing media such as, in particular, polymer melts, polymer solutions and dispersions and also devolatilisation apparatuses for carrying out the abovementioned process.

The present invention relates to a process for devolatilisingpolymer-containing media such as, in particular, polymer melts, polymersolutions and dispersions and also devolatilisation apparatuses forcarrying out the abovementioned process.

Extrusion is a frequently employed process in the preparation, treatmentand processing of polymers. Here and in the following, extrusion is thetreatment of a medium in a single-screw or multiscrew extruder.

In the preparation of polymers, extrusion is employed industrially forremoving volatile constituents such as monomers, oligomers and alsoauxiliaries and solvents from polymer-containing media ([1], p. 192 to212; [1]=Klemens Kohlgrüber. Twin-Screw Extruders, Hanser Verlag Munich2007). Furthermore, chemical modification of the polymer, e.g. bygrafting, modification of functional groups or modification of themolecular weight by targeted increase or decrease of the molecularweight can optionally also be carried out during extrusion or thepolymer can, for example, be finished by mixing in of additives.

The advantages of extrusion are offset by the disadvantage that aparticularly large amount of energy is dissipated in thepolymer-containing media to be extruded, especially in the intermeshzones of the screw elements typically used as treatment element in theextruders, which can lead to severe local overheating. This localoverheating can lead to damage to the product, e.g. change of odour,colour, chemical composition, or to formation of inhomogeneities in theproduct, e.g. gel particles or specks.

Damage patterns in various polymers in the case of local overheatingare, for example, described in WO2009/153000 A on p. 22, line 7 to p.24, line 25.

Rubbers such as polybutadiene (BR), natural rubber (NR), polyisoprene(IR), butyl rubber (IIR), chlorobutyl rubber (CIIR), bromobutyl rubber(BIIR), styrene-butadiene rubber (SBR), polychloroprene (CR),butadiene-acrylonitrile rubber (NBR), partially hydrogenatedbutadiene-acrylonitrile rubber (HNBR) and ethylene-propylene-dienecopolymers (EPDM), in particular, tend to display crosslinking and gelformation if the temperature is too high, which leads to a severedeterioration in mechanical properties of the products producedtherefrom. In the case of chlorobutyl and bromobutyl rubber and alsochloroprene rubbers, corrosive hydrogen chloride or hydrogen bromide canbe liberated at elevated temperature and this in turn catalyzes thefurther decomposition of the polymer.

The reaction rate at which damage to the polymer proceeds depends on thetemperature and the reaction rate constant k(T) for this can bedescribed by the Arrhenius equation:k(T)=A*exp(−E _(A)/(R*T)).

In this equation, k is the reaction rate constant, T is the absolutetemperatuer in [K], A is the frequency factor, E_(A) is the activationenergy in [J/mol] and R is the universal gas constant in [J/(mol*K)].

Processes for the extrusion of polymer-containing media should thereforegenerally be configured, also from an energy point of view, so that theaverage temperature increase is as low as possible and local temperaturepeaks as occur, for example, in the intermesh zones of a screw elementhaving a classical Erdmenger screw profile according to the prior art,are avoided.

The prior art contains a large number of approaches to solving thisproblem.

DE 1 180 718 A discloses a twin-screw machine having single-flightedtreatment or screw elements. In cross section, the outer contour of thescrew elements is made up of circular arcs. The active flank in thedirection of rotation has an outer contour which is made up of threecircular arcs whose midpoints are located either on the outer radius oron the longitudinal axis of the screw elements. A disadvantage is thatthe screw elements allow only a small flexibility in the setting of theshearing and/or elongating flows acting on the material to be processed.

WO2009/152968 and WO2011/039016 disclose treatment elements forextruders, in particular screw elements, which due to their roundedshape cause less energy input into polymer-containing media duringextrusion.

EP 1 617 985 A1 discloses a treatment plant and also a process fordevolatilising bimodal polyolefins. In the treatment plant, twocorotating twin-screw extruders are arranged in series and the secondextruder viewed in the transport direction has a devolatilisation zonefor devolatilising the polyolefins to be treated. A disadvantage of thistreatment plant is that the devolatilisation performance, i.e. theproportion of undesirable volatile constituents which is removed, islow.

EP 0861717 A1 discloses a process and an apparatus for processingmaterials which give off a large amount of volatiles. The extrusionapparatus has a main extruder and two secondary extruders which openlaterally into this, so that the gas stream formed in a vaporisationzone of the main extruder is divided into at least three substreamswhich are then discharged from the extruders.

EP 1 127 609 A2 discloses a process for removing volatile constituentsfrom a polymer-containing medium using a kneader. Here, the energy ispartly introduced through the wall of the kneader and used forvaporising the solvent. Furthermore, energy is introduced as mechanicalenergy by means of the rotating screw of the kneader. The introductionof mechanical energy via the kneader depends greatly on the viscosity ofthe product, which greatly reduces the flexibility and thusattractiveness of the process for industrial use.

EP 1 165 302 A1 discloses an apparatus and a process for devolatilisingplastics, which has a backward-devolatilisation zone and a plurality ofdevolatilisation zones in the transport direction, which are operatedunder reduced pressure. The reduced pressure is necessary in order toachieve low residual concentrations of volatile constituents.

“Process Machinery”, parts I and II, March and April 2000; author: C. G.Hagberg, and WO2010/031823 A and PCT/EP2011/054415 disclose the directdevolatilisation of rubber solutions using a flash tank and one or moreextruders.

U.S. Pat. No. 4,055,001 discloses a process for preparing polymers suchas butyl rubber having a water content of less than 0.1% by weight usingultrasonic probes during the drying process. However, the very highshear stress produced by ultrasound is unfavourable for industrial use.

US 2001/056176 A1 discloses a single-stage process for concentratingrubber solutions. The rubber solution is heated by means of steam inorder to remove solvents present in one step by devolatilisation underreduced pressure, producing white crumbs. US 2001/056176 A1 recommends alarge-volume stream of steam to remove volatile components at a lowvapour pressure and leads to undesirable inclusion of additional waterin the crumbs.

However, the abovementioned approaches to solving the problem for theextrusion of polymer-containing media, in particular rubber-containingmedia, are still capable of improvement.

It was therefore an object of the invention to provide a process forremoving volatile constituents from polymer-containing media, whichmakes possible a high devolatilisation performance combined with a highpolymer throughput together with a low residual content of volatileconstituents.

The invention then provides an apparatus which is particularly suitablefor removing volatile compounds from polymer-containing media and has atleast one extruder which in turn has:

-   -   a barrel and n barrel holes B_(n) having the associated hole        diameters D_(n) where n is an integer, preferably an integer        from 1 to 16, particularly preferably from 1 to 12, very        particularly preferably from 2 to 8 and even more preferably 2,        and the barrel holes in the case of n being greater than 1        preferably pass through opposite one another and are likewise        preferably arranged parallel to one another,    -   one or more screws W_(n) which can be driven so as to rotate and        are in each case arranged concentrically in one of the barrel        holes B_(n), have an axis of rotation A_(n) and are equipped        with treatment elements whose cross-sectional profile in the        circumferential direction has        -   m relative maxima R^(m) _(max n) in respect of the radial            dimension of the cross-sectional profile to the axis of            rotation A_(n) of the screw W_(n), where m is an integer            from 1 to 8, preferably from 1 to 4, particularly preferably            1, 2 or 3, very particularly preferably 1 or 2 and even more            preferably 2,        -   a maximum value R_(max n) in respect of the radial dimension            of the cross-sectional profile to the axis of rotation A_(n)            of the screw W_(n), where R_(max n) fulfils:            R _(max n)<=(D _(n)/2)    -   at least one feed zone,    -   one or more devolatilisation zones comprising in each case at        least one devolatilisation opening which is suitable for        discharge of volatile constituents from a polymer-containing        medium from the extruder,    -   at least one discharge zone,        where the extruder has screw elements having a pitch t as        treatment elements, which are configured so that at least two of        the following three conditions are met:

-   S1) the cross-sectional profile has at least one relative maximum    R^(m) _(max n) based on the radial dimension of the profile curve,    for which:    -   0.420 D_(n)<R^(m) _(max n)<0.490 D_(n), preferably 0.430        D_(n)>=R^(m) _(max n), <0.485 D_(n), particularly preferably        0.440 D_(n)<R^(m) _(max n), <0.482 D_(n) and particularly        preferably 0.450 D_(n)<R^(m) _(max n)<0.480 D_(n),

-   S2) 1.38 D_(n)<t<5.00 D_(n), preferably 1.60 D_(n)<t<3.00 D_(n),    particularly preferably 1.80 D_(n)<t<2.50 D_(n) and very    particularly preferably 1.90 D_(n)<t<2.40 D_(n),

-   S3) the cross-sectional profile of the respective screw element has    no tangential angle β greater than 30°, preferably greater than 25°,    particularly preferably 22°, very particularly preferably 15° and    very particularly preferably 10°, on the active flanks located at    the front in the direction of rotation in the range of the radial    dimension from 0.95 R_(max) to R_(max), preferably from 0.90 R_(max)    to R_(max), particularly preferably from 0.80 R_(max) to R_(max),    very particularly preferably from 0.50 R_(max), to R_(max) and even    more preferably in the entire range from 0 to R_(max), where the    tangential angle β is defined as    -   the smaller of the two angles formed on drawing the tangents at        any point on the cross-sectional profile of the treatment        element at which the cross-sectional profile cannot be        continually differentiated    -   and is 0° at any point on the cross-sectional profile of the        treatment element at which the cross-sectional profile can        always be differentiated.

The scope of the invention encompasses not only the features andcombinations of features which are explicitly mentioned but also anycombinations of preferred ranges which are specified for each feature.

For the purposes of the invention, the cross-sectional profile is theprofile of a treatment element, in particular a screw element, in aplane orthogonal to the axis of rotation A_(n) of the screw on which thetreatment element is arranged.

The term screw elements encompasses both the modular construction whichis nowadays customary comprising a core shaft and screw elements whichhave an accommodation opening for the core shafts and also screws havinga solid construction, e.g. in one-piece form, screws which consist ofindividual subsegments which are produced in solid construction, orcombinations of the abovementioned constructions.

The abovementioned geometric ratios are described by means of aclassical two-flighted Erdmenger profile for a tightly intermeshingtwin-screw extruder, as is shown in FIG. 1. The Erdmenger profile has,for example, two relative maxima R¹ _(max) and R² _(max) in the regionof intermeshing of the screws which in each case have the maximum valueR_(max) in respect of the radial dimension of the cross-sectionalprofile to the axes of rotation A1 and A2.

In the literature, screw elements which have p relative maxima R^(p)_(max) which are each at least 85%, preferably at least 95%, of themaximum value R_(max) in respect of the radial dimension of thecross-sectional profile to the axis of rotation A_(n) of the screw W_(n)are generally also referred to as p-flighted screw profile.

The active flanks located at the front in the direction of rotation arefor the purposes of the present invention those regions of thecross-sectional profile of the screw elements from a relative maximumR^(m) _(max n) to the next relative minimum R^(m) _(min n) in respect ofthe radial dimension of the cross-sectional profile to the axis ofrotation A_(n) of the screw W_(n) in the direction of rotation. If therelative maximum R^(m) _(max n) or the relative minimum R^(m) _(min n)is a single point, this is by definition neither a constituent of theactive flank (F_(akt)) nor of the passive flank F_(pass). The sameapplies to the midpoint M of an intermesh region which has, for example,a plateau-like relative maximum in respect of the function R(φ) of thescrew profile, where φ is the angle in the circumferential direction tothe axis of rotation A, over an intermesh angle KW. In this case, asshown in FIG. 1, the region from the midpoint of the plateau-likemaximum to the end point of the relative maximum in the direction ofrotation of the screw element is by definition likewise part of theactive flank F_(akt). The end point of the relative maximum in thedirection of rotation of the screw element is the point of theintersection Sp in the Erdmenger profile shown in FIG. 1.

Furthermore, the radius 0.9 R_(max), is indicated by way of example inFIG. 1, from which it can be seen that the intersection point Sp of theintermesh circular arc and the flank circular arc is located outsidethis radius, i.e. between 0.9 R_(max), and R_(max), and produces a kinkin the profile which generates an edge on the screw element. Thetangents T1 of the intermesh circular arc and T2 of the flank circulararc and also the smaller angle β enclosed by the tangents T1 and T2,which for the Erdmenger profile shown is about 34°, are likewise shownin FIG. 1.

The Erdmenger profile shown therefore does not satisfy feature S3).

The feature S1) is also described as radial play in the literature.

According to the invention, polymer-containing media are media whichcomprise at least one polymer and at least one volatile compound.

Polymers can be natural or synthetic polymers, preferably ones having aweight average molecular weight of more than 2000 g/mol, particularlypreferably more than 5000 g/mol.

Examples of natural and synthetic polymers encompass thermoplasticpolymers such as polycarbonates, polyamides, polyesters, in particularpolybutylene terephthalate and polyethylene terephthalate, polylactides,polyethers, thermoplastic polyurethanes, polyacetals, fluoro polymers,in particular polyvinylidene fluoride, polyether sulphones, polyolefins,in particular polyethylene and polypropylene, polyimides, polyacrylates,in particular poly(methyl) methacrylate, polyphenylene oxide,polyphenylene sulphide, polyether ketone, polyaryl ether ketone, styrenepolymers, in particular polystyrene, styrene copolymers, in particularstyrene-acrylonitrile copolymer, acrylonitrile-butadiene-styrene blockcopolymers, and polyvinyl chloride and also elastomers such as rubbersfrom the group consisting of styrene-butadiene rubbers, natural rubbers,butadiene rubbers, isoprene rubbers, ethylene-propylene-diene rubberssuch as ethylene-propylene-diene (M class) rubbers (EPDM),ethylene-propylene rubbers, butadiene-acrylonitrile rubbers,hydrogenated nitrile rubbers, butyl rubbers, halobutyl rubbers,chloroprene rubbers, ethylene-vinyl acetate rubbers, polyurethanerubbers, guttapercha, fluoro rubbers, silicone rubbers, sulphiderubbers, chlorosulphonyl-polyethylene rubbers and also any mixtures ofthe abovementioned thermoplastic polymers and elastomers.

In the context of the present invention, the term butyl rubber refers,in particular, to a copolymer of isobutene (2-methylpropene) andisoprene (2-methylbuta-1,3-diene). On a molar basis, the isoprenecontent of the polymer is in the range from 0.001 to 5%, preferably from1.8 to 2.3 mol %. Butyl rubber consists of linear polyisobutene chainswith randomly distributed isoprene units. The isoprene units introduceunsaturated positions into the polymer chain, which makes vulcanisationpossible. The mass average molecular weight of butyl rubber Mw isusually in the range from 50 000 to 1 000 000 g/mol, preferably from 300000 to 1 000 000 g/mol.

Halogenated butyl rubbers additionally contain a certain amount ofhalogen which is chemically bound to the polymer. The amount ofchemically bound halogen is usually in the range from >0 to 3% by weightbased on the total mass of the polymer. The (halo)butyl rubbers can alsocontain additives, e.g. from 0.0001 to 4 phr (phr=parts per hundredparts of rubber based on the weight of the rubber), of epoxidisedsoybean oil (ESBO), from 0.0001 to 5 phr of calcium stearate and from0.0001 to 0.5 phr of antioxidants. Other additives can likewise beemployed, depending on the use of the butyl rubber product, i.e. fillersor colorants.

In the case of bromobutyl rubber, the typical bromine content in thefinished product is from 1.5 to 2.5% by weight, preferably from 1.6 to2.0% by weight.

In the case of chlorobutyl rubber, the typical chlorine content in thefinished product is from 1.0 to 1.5% by weight, preferably from 1.15 to1.35% by weight.

The polymer-containing media to be used according to the invention can,for example, be in the form of suspensions, pastes, melts, solutions,particulate solid compositions or mixed forms of the abovementionedtypes.

For the purposes of the present invention, the term “volatile compounds”refers to compounds having a boiling point below 250° C. at a pressureof 1013 hPa. Volatile compounds are, in particular, water and othervolatile inorganic compounds and also volatile, organic compounds.Volatile organic compounds are typically solvents which are used in thepolymerisation or in subsequent processing steps, monomers or oligomerswhich, for example, originate from the polymerisation process of otherorganic compounds such as additives.

The extruder preferably has a barrel and n=1 to 16, particularlypreferably n=1 to 12, very particularly preferably n=2 to 8 and evenmore preferably n=2, barrel holes B_(n).

When n is greater than 1, the barrel holes B_(n) preferably pass throughopposite one another and are likewise preferably arranged parallel toone another. Embodiments in which n is greater than 1 and the barrelholes do not pass through and are preferably parallel comprise apossible embodiment of the invention.

Types of extruder which are suitable for the purposes of the inventionthus encompass single-screw and multiscrew extruders, for exampletwin-screw extruders or ring extruders, with twin-screw extruders beingpreferred. Twin-screw extruders can be driven in a contrarotating orcorotating manner. Preference is given to multiscrew extruders such as,in particular, twin-screw extruders or ring extruders equipped withclose-intermeshing treatment elements, in particular self-cleaning screwelements. Multiscrew extruders can also be extruders having extruderscrews or treatment elements which do not intermesh and do not come intocontact with one another.

In one embodiment, the at least one extruder of the devolatilisationapparatus also has at least one dispersing zone. In the dispersing zone,it is possible, for example, for stripping agents or other additives tobe introduced into the polymer. The treatment elements of the dispersingzone can, for example, be kneading elements, toothed blocks, tootheddiscs or toothed mixing elements. A possible further selection ofsuitable elements may be found in [1].

In the region of the active flank of a screw element, thepolymer-containing medium to be extruded is pressed into an evernarrower wedge in the barrel hole B_(n) of the extruder screw W_(n) onrotation of the extruder screw W_(n). Shearing and elongating flowsoccur here and lead, particularly in the case of devolatilisationaccording to the invention, to a high degree of surface renewal and thusto improved diffusion of volatile constituents from thepolymer-containing medium.

It has surprisingly been found that the throughput and devolatilisationperformance of extruders can be improved significantly when screwelements which conform to two of the features S1), S2) and S3), forexample S1) and S2) or S2) and S3) or S1) and S3), or preferably allthree of the features S1), S2) and S3) are present as treatment elementsin the extruder.

In an embodiment, the features S1) and S2) or all three features S1),S2) and S3) are satisfied.

It has been found that screw elements which satisfy the above-describedcombinations of the features S1), S2) and S3) keep the energy input solow that the above-described damage to the extruded polymers can belargely or completely avoided despite a high devolatilisationperformance. This effect is then fully utilized, in particular, when thescrew elements having the abovementioned features are used in at leastone devolatilisation zone. Preference is given to at least the lastdevolatilisation zone of the extruder being equipped with correspondingscrew elements. In a further embodiment, all devolatilisation zones ofthe extruder are equipped with corresponding screw elements. The numberof devolatilisation zones is in principle not subject to anyrestrictions and can be, for example, from 1 to 20, preferably from 1 to10 and particularly preferably from 2 to 8. The devolatilisation zonesare typically downstream of the feed zone of the extruder, thearrangement of at least one devolatilisation zone upstream of the feedzone of the extruder (referred to as backwards devolatilisation zone) ispreferred.

Devolatilisation zones typically have, as is known to those skilled inthe art, at least one devolatilisation opening in the extruder barrelwhich open(s) into devolatilisation domes which are in turn connectedvia gas discharge lines to a condenser unit in which the volatilecompounds given off from the polymer-containing media are condensed. Thepressure in the devolatilisation zones for the devolatilisation domes ispreferably regulated by means of pumps, in particular vacuum pumps.

The volatile compounds given off from the polymer-containing medium viathe devolatilisation openings and the devolatilisation domes tend tocarry polymers or products with them, which in the worst case can leadto blockage of the devolatilisation openings and of the devolatilisationdomes.

The devolatilisation openings and the devolatilisation domes are, in apreferred embodiment of the invention, therefore configured so that theyeffectively prevent or reduce exit of polymer-containing medium orproduct.

Suitable means for achieving this are single-screw or multiscrew, inparticular twin-screw, stopping screws which are mounted on thedevolatilisation openings and are operated so as to transport into theextruder or rollers or belts which are arranged on the inside of thedevolatilisation openings in order to push polymer-containing medium orproduct back into the extruder. As an alternative to or in addition tothe abovementioned means, it is possible to use coatings on thedevolatilisation openings which reduce or prevent adhesion of thematerial to the surface. Suitable coatings are, for example, DLC(diamond-like carbon), ethylene-tetrafluoroethylene (ETFE),polytetrafluoroethylene (PTFE) and nickel alloys.

The pressure in the devolatilisation openings and devolatilisation domesis, for example, in the range from 1 hPa and 2000 hPa, preferably from 5hPa to 900 hPa.

If a plurality of devolatilisation zones are arranged downstream of thefeed zone of the extruder, it is necessary to install pressure buildupzones and preferably additionally banking-up elements between theindividual devolatilization zones in order to seal off the individualdevolatilisation zones from one another and thus allow progressivedegassing in the transport direction of the extruder. In this case, thedevolatilisation zones can be operated at different pressures, inparticular at pressures which typically become lower in the transportdirection of the extruder.

While devolatilisation zones are typically partly filled zones having avolumetric degree of fill of from about 0.1 to 0.6, preferably from 0.3to 0.5, a volumetric degree of fill of 1 is achieved in the pressurebuildup zones and optionally at the banking-up element. These are thenreferred to as fully filled zones or sections.

As treatment elements in the pressure buildup zones, it is possible touse, for example, conventional screw elements having a smaller pitch tthan in the devolatilisation zones.

As banking-up elements, it is possible to use, for example,backwards-transporting elements, forwards-transporting elements having asmall pitch, kneading blocks, banking-up discs, toothed mixing elementsor elements in general having a low transport volume.

The extruder can, for example, also have at least one dispersing zone,for example in order to introduce stripping agents or other additivesinto the polymercontaining medium. It has surprisingly been found thatthe dispersion in the extruder functions particularly well when the atleast one dispersing zone has, as treatment elements, screw elementswhich have a pitch t and are configured so that at least two of thethree following conditions are satisfied:

-   S1) having the abovementioned values including the preferred ranges    for these-   S3) having the abovementioned values including the preferred ranges    for these-   S4) 1.50 D_(n)<t<12.00 D_(n), preferably 1.60 D_(n)<t<10.00 D_(n)    and particularly preferably 2.00 D_(n)<t<9.00.

If stripping agents are to be introduced into the polymer-containingmedium to promote devolatilisation, the dispersion zones are preferablyarranged upstream of the devolatilisation zones of the extruder.

In one embodiment, the devolatilisation zones are located upstream of atleast some depressurisation elements.

Depressurisation elements can be, for example, rotating or fixedperforated plates.

Such perforated plates are known, for example, from JP 59 048136 A, U.S.Pat. No. 3,501,807, DE 34 31 063, DE 623 903 and PCT/EP2011/062636.

As depressurisation elements, it is also possible to use, for example,backwards conveying elements, forwards conveying elements having a verysmall pitch, kneading blocks or banking-up discs.

In a preferred embodiment, use is made of fixed perforated plates whichin operation are fixed to but removable from the barrel and each have anaccommodation opening for accommodation of each screw present in theextruder and preferably act as a sliding seal for the screws. The radialspacing s of the accommodation opening to the screw in relation to thebarrel hole B is preferably such that 0.001≦s/D≦0.02, preferably0.002≦s/D≦0.01 and particularly preferably 0.003≦s/D≦0.006.

The perforated plates have one or more, preferably a large number, ofholes, where the holes have a diameter d of, for example, from 1 mm≦d≦6mm, preferably 1.5 mm≦d≦5 mm and particularly preferably 2 mm≦d≦4 mm.

In a likewise preferred embodiment, the perforated plates are made up ofa plurality of parts, preferably two parts, so that they can be takenfrom the barrel without removal of the screws.

The particular advantage of the use of perforated plates is that thepolymer-containing medium passed through the perforated plates is in theform of strands in the subsequent free space of the devolatilisationzone and has a larger surface area compared to the polymer-containingmedium upstream of the die plate. As a result, volatile compounds caneasily leave the polymer-containing medium and be separated from thelatter.

In general, the extruder can comprise one or more feed openings for theintroduction of additives, and these can in principle be positionedeverywhere in the extruder, preferably outside the devolatilisationzones and preferably in the dispersing zones, if present.

Examples of additives which can be introduced via the feed openings, inparticular for (halo)butyl rubber products encompass stabilizers, acidscavengers such as ESBO (epoxidized soybean oil), stearates such ascalcium stearate, antioxidants and the like. Examples of suitableantioxidants contain sterically hindered phenols such asbutylhydroxytoluenes and derivatives thereof, e.g. Irganox 1010 and1076, amines, mercaptobenzimidazoles, certain phosphites and the like.

As an alternative or in addition, the additives can also be introducedinto the polymeric medium PM before entry into the devolatilisationapparatus or, if they are liquid, with the stripping agents in theextruder.

Screw elements which can satisfy feature S3) are in principle knownfrom, for example, WO2009/152968 A and WO2011/039016 A.

According to the invention, preference is given to using screw elementswhose cross-sectional profile can be represented completely by a profilecurve which can continually be differentiated. Such cross-sectionalprofiles are preferably two-flighted or three-flighted. Thecross-sectional profile of such screw elements will hereinafter also bereferred to as screw profiles.

Particular preference is given to using abovementioned screw elements inclose-intermeshing multiscrew extruders such as, in particular,twin-screw extruders, preferably corotating twin-screw extruders.

The cross-sectional profiles of such screw elements can be unambiguouslydescribed by an arrangement of circular arcs and in their totality arecomposed of n circular arcs, where n is greater than or equal to four.Each of the n circular arcs has a starting point and an end point. The ncircular arcs go tangentially into one another at their starting pointsand end points, so that together they form a profile curve which can becontinually differentiated.

The position of each circular arc j (j=1 to n) can be fixedunambiguously by the reporting of two different points. The position ofeach circular arc is advantageously fixed by indication of the midpointand the starting point or end point. The size of an individual circulararc j is fixed by the radius r_(j) and the angle a_(j) at the midpointbetween starting point and end point, where the radius r_(j) is greaterthan 0 and less than the spacing a between the axes of the screws andthe angle a_(j) in radians is greater than or equal to 0 and less thanor equal to 2p; where p is the number pi.

The abovementioned screw elements are characterized in that

-   -   the generating screw profile and the screw profile generated lie        in one plane,    -   the axis of rotation of the generating screw profile and the        axis of rotation of the screw profile generated are at a spacing        a (axial spacing) in each case perpendicularly on said plane of        the screw profiles, where the intersection of the axis of        rotation of the generating screw profile with said plane is        referred to as point of rotation of the generating screw profile        and the intersection of the axis of rotation of the screw        profile generated with said plane is referred to as point of        rotation of the screw profile generated,    -   the number of circular arcs of the total generating screw        profile n is greater than or equal to four (n>4),    -   the outer radius ra of the generating screw profile is greater        than zero (ra>0) and less than the axial spacing (ra<a),    -   the core radius ri of the generating screw profile is greater        than zero (ri>0) and less than or equal to ra (ri≦ra),    -   all circular arcs of the generating screw profile go into one        another tangentially,    -   the circular arcs form a closed screw profile, i.e. the sum of        the angles a_(j) of all circular arcs j is equal to 2p; where p        is the number pi,    -   the circular arcs form a convex screw profile,    -   each of the circular arcs of the generating screw profile is        within or on the boundaries of an annulus which has the outer        radius ra and the core radius ri and whose midpoint is on the        point of rotation of the generating screw profile,    -   at least one of the circular arcs of the generating screw        profile contacts the outer radius ra of the generating screw        profile at a point P_(A),    -   at least one of the circular arcs of the generating screw        profile contacts the core radius ri of the generating screw        profile at a point P_(I) and the number of circular arcs n′ of        the screw profile generated is equal to the number of circular        arcs n of the generating screw profile,    -   the outer radius ra′ of the screw profile generated is equal to        the difference between the axial spacing and core radius ri of        the generating screw profile (ra′=a−ri),    -   the core radius ri′ of the screw profile generated is equal to        the difference between the axial spacing and outer radius ra of        the generating screw profile (ri′=a−ra),    -   the angle a_(j)′ of the j′-th circular arc of the screw profile        generated is equal to the angle a_(j) of the j-th circular arc        of the generating screw profile, where j and j′ are integers        which together go through all values in the range from 1 to the        number of circular arcs n or n′,    -   the sum of the radius r of the j′-th circular arc of the screw        profile generated and the radius j of the j-th circular arc of        the generating screw profile is equal to the axial spacing a,        where j and j′ are integers which together run through all        values in the range from 1 to the number of circular arcs n or        n′,    -   the midpoint of the j′-th circular arc of the screw profile        generated is at a spacing from the midpoint of the j-th circular        arc of the generating screw profile which is equal to the axial        spacing a and the midpoint of the j′-th circular arc of the        screw profile generated is at a spacing from the point of        rotation of the screw profile generated which is equal to the        spacing of the midpoint of the j-th circular arc of the        generating screw profile from the point of rotation of the        generating screw profile and the connecting line between the        midpoint of the j′-th circular arc of the screw profile        generated and the midpoint of the j-th circular arc of the        generating screw profile is parallel to a connecting line        between the point of rotation of the screw profile generated and        the point of rotation of the generating screw profile, where j        and j′ are integers which together run through all values in the        range from 1 to the number of circular arcs n or n′,    -   a starting point of the j′-th circular arc of the screw profile        generated is in a direction based on the midpoint of the j′-th        circular arc of the screw profile generated which is opposite to        the direction which has a starting point of the j-th circular        arc of the generating screw profile based on the midpoint of the        j-th circular arc of the generating screw profile, where j and        j′ are integers which together run through all values in the        range from 1 to the number of circular arcs n or n′.

The screw elements can be unsymmetrical or symmetrical, with preferencebeing given to symmetrical screw elements. Symmetrical screw elementscan be axially symmetric or point-symmetric; preference is given toaxially symmetric screw elements according to the invention.

The generation of such cross-sectional profiles is described in detailin WO2009/152968 A and WO2009/153000 A and is thus known to thoseskilled in the art.

In another embodiment of the invention, screw elements whosecross-sectional profiles are hereinafter also referred to as outercontour and which satisfy the feature S3) and have

-   -   a longitudinal axis M*,    -   a core radius Rj and an outer radius R_(a) which each have the        longitudinal axis M* as midpoint,    -   an outer contour A(φ) running around the longitudinal axis M*,        where φ is the angle around the longitudinal axis M* and    -   R_(i)<D_(A)((p)<R_(a) for a spacing D_(A)((p) of the outer        contour A(φ) from the longitudinal axis M,        and are further characterized in that    -   the outer contour A(φ) has at least one outer contour section        A(Δφ) which runs along an angular section Δφ and has a        continually changing spacing D_(A)(Δφ) from the longitudinal        axis M*, where Rj<D_(A)(Δφ)<R_(a), and    -   has an associated evolute E,    -   which is a number of n points P(i) where i=1 to n and n≧3,    -   where each of the points P(i) is located outside the        longitudinal axis M* and within the outer radius R_(a), and    -   each two adjacent points P(i) and P(i+1) have a spacing Δr(i)        from one another which is less than R_(i)/2,        are used according to the invention.

The screw elements are preferably further characterized in that each twoadjacent points P(i) and P(i+1) have a spacing Δr(i) from one anotherwhich is less than R_(i)/4, in particular less than R_(i)/6 and inparticular less than R_(i)/8, where the two adjacent points P(i) andP(i+1) belong to adjacent evolvent curves E′(i) and E′(i+1).

In another embodiment, the screw elements are characterized in that eachtwo adjacent points P(i) and P(i+1) have a constant spacing Dr from oneanother and optionally also in that the evolvent curves E′(i) belongingto the points P(i) each have a central angle Δε(i) which is less than60°, in particular less than 45° and in particular less than 30°.

In a further embodiment, the screw elements are characterized in thatthe evolvent curves E′(i) belonging to the points P(i) have constantcentral angles Δε.

In a further embodiment, the screw elements are characterized in thatthe points P(i) are located on a continuous curve which can bedifferentiated and has a constant curvature direction, and in a furtherembodiment the evolutes E draw the same curve at least in sections.

In a further embodiment, the screw elements are characterized in thatthe at least one outer contour section A(Δφ) is curved over the entireangle section Δφ.

In a further embodiment, the screw elements are characterized in thatthe outer contour A(φ) has at least two outer contour sectionsA(A(φ_(j)) and A(A(φ_(j+1)) and the at least two associated evolutesE_(j) and E_(j+1) are different.

In a further embodiment, the screw elements are characterized in thatthe outer contour A(φ) has a uniform direction of curvature.

The abovementioned cross-sectional profiles are preferably alsotwo-flighted or three-flighted.

The generation of such cross-sectional profiles is described in detailin WO2011/039016 A and is thus known in principle to those skilled inthe art.

The abovementioned screw elements are particularly preferably used inclosely intermeshing multiscrew extruders such as, in particular,twin-screw extruders, preferably corotating twin-screw extruders.

The feature S2) can be satisfied by adhering to particular radial playsor spacings between the barrel holes B_(n) and the screw elements of thescrew, rotating in this barrel hole B_(n) in a manner known per se byappropriate manufacture of the screw elements.

The radial plays can, as is known to those skilled in the art, beconstant or, within the limits indicated, be variable. It is alsopossible to shift a screw profile within the radial plays. A personskilled in the art will know of methods of deriving a screw profilehaving plays according to the invention from a predetermined, preciselyscraping screw profile. Methods known for this are, for example, thepossibilities of axial spacing enlargement, longitudinal sectionequidistants and volume equidistants described in [1] on page 28 ff. Inthe case of axial spacing enlargement, a screw profile having arelatively small diameter is constructed and expanded by the absolutemagnitude of the play between the screws. In the method of longitudinalsection equidistants, the longitudinal section profile curve (parallelto the axis of rotation of the respective element) is shiftedperpendicularly inward to the profile curve by half the screwelement-screw element play in the direction towards the axis ofrotation. In the method of volume equidistants, the screw element isreduced in size by half the screw to screw play in the directionperpendicular to the surfaces of the precisely scraping profile,proceeding from the volume curve on which the srew elements are cleaned.Preference is given to using the methods of longitudinal sectionequidistants and volume equidistants, particularly preferably volumeequidistants, are preferably used.

Satisfying the feature S1) is a simple question of manufacture andadequately known to those skilled in the art.

Preferred materials of which the screw elements generally consist aresteels, in particular nitriding steels, chromium steels, tool steels andstainless steels, and also powder-metallurgically produced metalliccomposites based on iron, nickel or cobalt. Further examples arenickel-based alloys and non-metallic materials such as ceramics.

The devolatilisation apparatus of the invention can also comprise apreextruder or prekneader installed upstream of the extruder, which arein each case configured as a devolatilisation extruder ordevolatilisation kneader.

Such arrangements are known in principle from EP 2 353 839 A orPCT/EP2011/054415.

In one embodiment of the devolatilisation apparatus, the transition zoneconnecting the devolatilising preextruder or devolatilising prekneaderand the (main) extruder can have at least one, preferably precisely one,depressurisation element such as, in particular, the above-described dieplates.

In a further embodiment of the devolatilisation apparatus, thetransition zone connecting the devolatilising preextruder ordevolatilising prekneader and the (main) extruder can contain at leastone pressure regulating unit, for example an orifice plate, by means ofwhich the energy input into the preextruder or prekneader can then becontrolled.

This two-stage structure of the devolatilisation apparatus enables ahigh devolatilisation performance combined with a high throughput ofpolymer-containing medium to be achieved.

If a devolatilising preextruder is used, the selected speed of rotationof this is typically high, since the energy input is low because of the(still) low viscosity of the polymer-containing medium to bedevolatilised. The proportion of volatile compounds can in this way beconsiderably reduced before introduction into the (main) extruder.

One or more further concentrator units can be installed upstream of thedevolatilising preextruder or devolatilising prekneader in order toincrease the devolatilisation performance further.

Such concentrator units can be, for example, flash evaporators orcyclones which are adequately known from the prior art.

In one embodiment, a concentration unit comprises at least

-   -   a heating device in combination with a devolatilisation tank,        where the bottom part of the devolatisation tank is connected to        a pump and the upper part of the devolatilisation tank is        connected to at least one gas discharge line,    -   a heating zone in combination with the pump of the concentration        unit and the feed zone of the extruder or of the preextruder or        of the prekneader.

In the context of the present invention, the term “in combination”refers to direct or indirect connections, with indirect connectionsbeing able to be effected, for example, via hoses or pipes.

The term “in combination” also allows for the option of further units ormeans being arranged between the units or means which are incombination.

Corresponding concentrator units are adequately known from WO2010/031823A.

Further features, advantages and details of the invention may be derivedbelow from the description of the examples.

The devolatilisation apparatus of the invention, including theembodiments thereof described above and below, is particularly suitablefor use in a process for devolatilising polymer-containing media, andthe invention therefore further provides a process for removing volatilecompounds from a polymer-containing medium (PM) which contains at leastone polymer and at least one volatile compound, which process comprisesat least the following steps:

-   -   a) provision of a devolatilisation apparatus according to the        invention,    -   b) introduction of the polymer-containing medium (PM) into the        devolatilisation apparatus which is operated so that volatile        compounds are given off from the polymer-containing medium (PM)        through the devolatilisation openings of the devolatilisation        unit and the polymer-containing medium (PM) is in this way        depleted in volatile compounds and the polymer is isolated as        product P from the polymer-containing medium on discharge from        the devolatilisation apparatus and the product P then has a        lower proportion of volatile compounds than the        polymer-containing medium (PM) introduced into the        devolatilisation apparatus and preferably has a total        concentration of volatile compounds of less than 1% by weight,        preferably less than 0.5% by weight, based on the mass of the        polymer.

The polymer-containing medium PM, which is also referred to as cement,especially in the case of solutions of elastomers in organic solvents,contains, for example, from 3 to 98% by weight of a polymer and from 2to 97% by weight of volatile compounds, in particular an organic solventor an organic solvent and water, where the abovementioned componentsmake up to 90-100% by weight, preferably from 95 to 100% by weight, ofthe total mass of the polymer-containing medium.

The organic solvent can, for example, be selected from the groupconsisting of linear or branched alkanes having from 4 to 10 carbonatoms, preferably from 4 to 7 carbon atoms. More preferred solvents aresolvents containing or consisting of n-pentane, isopentane, n-hexane,cyclohexane, isohexane, methylcyclopentane, methylcyclohexane andn-heptane and also any mixtures comprising or consisting of thesealkanes.

In one embodiment, the polymer-containing medium PM fed into theextruder contains, for example, from 30 to 98% by weight of a polymerand from 2 to 70% by weight of volatile compounds, in particular organicsolvents or organic solvents and water, where the abovementionedcomponents together make up from 90 to 100% by weight, preferably from95 to 100% by weight, of the total mass of the polymer-containingmedium.

The polymer-containing medium PM fed into the extruder preferablycontains from 40 to 95% by weight of a polymer and from 5 to 60% byweight of volatile compounds, in particular organic solvents or organicsolvents and water, where the abovementioned components together make upfrom 90 to 100% by weight, preferably from 95 to 100% by weight, of thetotal mass of the polymer-containing medium.

If the devolatilisation unit comprises a devolatilising preextruder, adevolatilising prekneader or a concentrator unit upstream of theextruder, the polymer-containing medium PM fed into the devolatilisingpreextruder, the devolatilising prekneader or the concentrator unitcontains, for example, from 10 to 95% by weight of a polymer and from 5to 90% by weight of volatile compounds, preferably from 15 to 80% byweight of a polymer and from 20 to 85% by weight of volatile compoundsand particularly preferably from 15 to 70% by weight of a polymer andfrom 30 to 85% by weight of volatile compounds, where the volatilecompounds are, in particular, organic solvents or organic solvents andwater and the abovementioned components together make up from 90 to 100%by weight, preferably from 95 to 100% by weight, of the total mass ofthe polymer-containing medium.

It will be clear to a person skilled in the art that the content ofvolatile compounds in the polymeric medium PM on entry into thedevolatilising preextruder or the devolatilising prekneader is lowerthan on entry into the downstream extruder. The same applies analogouslyto the content of volatile compounds in the polymeric medium PM on entryinto a concentrator unit located upstream of a devolatilisingpreextruder or a devolatilising prekneader.

In this case, the polymer-containing medium PM fed into the concentratorunit preferably contains from 5 to 80% by weight of a polymer and from20 to 95% by weight of volatile compounds, more preferably from 10 to75% by weight of a polymer and from 25 to 90% by weight of volatilecompounds, where the volatile compounds are, in particular, organicsolvents or organic solvents and water and the abovementioned componentstogether make up from 90 to 100% by weight, preferably from 95 to 100%by weight, of the total mass of the polymer-containing medium.

In an embodiment of the invention, the extruders can either be heated totemperatures of up to 300° C. or alternatively cooled via the barrels.

In a preferred embodiment, the extruder comprises means of operatingseparate zones independently at different temperatures, so that thezones can either be heated, unheated or cooled.

Preferred extruder materials should not be corrosive and shouldessentially prevent contamination of the polymer-containing medium ofthe product P with metal or metal ions.

Preferred extruder materials contain nitriding steel, duplex steel,stainless steel, alloys based on nickel, composites such as sinteredmetals, hot isostatically pressed materials, hard abrasion-resistantmaterials such as stellites, metals coated with coatings consisting of,for example, ceramic, titanium nitride, chromium nitride anddiamond-like carbon (DLC).

The gas discharge lines of the devolatilisation zones can be connectedto a condensation system and are preferably so connected.

In general, the purpose of the condensation system is to collectvolatile compounds which are removed from the devolatilisation openingsvia the gas discharge lines and usually comprises a condenser and avacuum pump. Any condensation system known from the prior art can beused for effecting the recovery of volatile compounds.

In general, the condensed volatile compounds are preferably, optionallyafter carrying out a phase separation to separate the volatile organiccompounds from water, recirculated to a process for the preparation ofpolymer-containing media.

The devolatilisation apparatus can be followed by product processingapparatuses which preferably cool.

Cooling product processing apparatuses comprise all the apparatusesknown to those skilled in the art for this purpose, for examplepneumatic crumb conveyors with convective air cooling, vibrating crumbconveyors with convective air cooling, vibrating crumb conveyors havingcooled contact surfaces, belt conveyors with convective air cooling,belt conveyors having cooled belts, water spray apparatuses andunderwater pelletisation apparatuses in which the water functions ascooling medium.

The product P can then be processed further to final packaging andforward despatch. (Halo)butyl rubber is, for example, cooled to atemperature of or below 60° C., for example formed into bundles by meansof a hydraulic press and then packed in cardboard or wooden boxes fordespatch.

In general, an increased feed rate of the polymer-containing medium PMinto the feed zone of the extruder requires a corresponding increase inthe speed of rotation of the extruder. Furthermore, the speed ofrotation determines the residence time of the polymer-containing mediumPM. Thus, speed of rotation, feed rate and the extruder diameter areusually dependent on one another. The extruder is usually operated withthe dimensionless throughput V/n*d³ being set to from about 0.01 toabout 0.2, preferably to from about 0.015 to about 0.1, where V is thevolume flow rate, n is the speed of rotation expressed in revolutionsper minute and d is the effective diameter of the extruder. The maximumand minimum feed rates and speeds of rotation are determined, forexample, by the size of the extruder, the physical properties of thepolymer present in the polymer-containing medium PM and the targetvalues for the volatile compounds remaining in the polymer. However, theoperating parameters can be determined by a person skilled in the artfrom these properties with the aid of a few initial experiments.

In an embodiment of the invention, the extruder is operated at a feedrate of from 5 to 25 000, preferably from 5 to 6000, kilograms per hour.

In general, the devolatilisation in the extruder and also in thepreextruder or prekneader can be aided by addition of a stripping agentwhich is removed together with other volatile compounds. Even thoughthis stripping agent can in principle be introduced anywhere in theextruder unit, addition outside the devolatilisation zones, e.g. in oneor more pressure buildup zones or dispersion zones, is preferred.

Suitable stripping agents are substances which are inert towards thepolymer-containing medium (PM) and have a vapour pressure of greaterthan 100 hPa at 100° C.

For the purposes of the invention, the term “inert” means that thestripping agent does not react chemically or does not appreciably reactchemically with the polymers. Suitable stripping agents are nitrogen,carbon dioxide, noble gases, propane, butane, water or a mixture of theabovementioned substances. The amount of stripping agent can be from0.0001 to 10% by weight, preferably from 0.001 to 5% by weight and morepreferably from 0.1 to 2% by weight, based on the amount of polymerobtained at the discharge zone of the extruder.

The invention will be illustrated by way of example below with the aidof the figures, but without being restricted thereto.

FIG. 1 shows a conventional two-flighted Erdmenger screw profile havingthe geometric test criteria as described in detail at the outset.

FIGS. 2a, 2b, 2c and 2d show continually integratable screw profileswhich satisfy at least the feature S3).

The following conventions apply to FIGS. 2a, 2b, 2c and 2d : thecoordinates x and y have their origin at the point of rotation of one ofthe screws. All angles indicated are in radians. All other measurementsindicated are normalised to the spacing of the axes and are representedby upper case letters: A=a/a; Rj=r/a; RA=ra/a; etc.

Furthermore:

-   RG=normalised barrel radius,-   RA=normalised outer radius of the profile,-   RF=normalised outer radius of the screw to be manufactured,-   S=normalised play between the screws (gap),-   D=normalised play of the screw to the barrel.

FIGS. 2a, 2b, 2c and 2d show examples of profiles of screw elements usedaccording to the invention with plays which are according to theinvention. In FIG. 2a , the gap S in the mutual cleaning of the screwswas selected so as to be the same as the gap D in the cleaning of thebarrel. In FIG. 2b , the gap S is smaller than D and in FIGS. 2c and 2d, D is, conversely, smaller than S.

FIG. 3 depicts a screw element which satisfies the features S3) and S1).

The construction of the profile as such is disclosed in WO2011/039016,especially in FIG. 26 and the associated description. However, theradial maxima R¹ _(max), R² _(max) and R³ _(max) relative to thediameter of the barrel holes D1 and D2 were reduced so that the radialplays of the feature S1) were obtained. The radius R_(max) in this caseis 0.96 of the barrel diameter.

FIG. 4 depicts a screw element which satisfies the features S3) and S1).

The construction of the two-flighted profile as such is likewisedisclosed in WO2011/039016, especially in FIG. 22 and the associateddescription. However, the radial maxima R¹ _(max) and R² _(max) relativeto the diameter of the barrel holes D1 and D2 were reduced so that theradial plays of the feature S1) were obtained. The radius R_(max) is inthis case 0.96 of the barrel diameter.

Both in FIG. 3 and in FIG. 4, the relative maximum forming an edge,which at the same time in each case represents an absolute maximum, hasdegenerated to a relative point maximum, so that the tangential angle bobtained for these points remains outside consideration since the pointsby definition are not assigned to the active flank F_(akt).

FIG. 5 depicts the extruder of a devolatilisation apparatus according tothe invention in longitudinal section and the upstream prextruder incross section.

FIG. 6 shows the preextruder located upstream of the extruder inlongitudinal section.

The following examples are illustrated with the aid of FIGS. 5 and 6.

EXAMPLES

Analytical Methods

Water content of polymer-containing media PM: The sample was introducedinto a centrifuge and centrifuged at 4000 rpm at room temperature for 5minutes. The water was then collected at the bottom of the ampoule andweighed.

Total concentration of volatile compounds: A sample of the product (P)was cut into small pieces having a size of 2×2 mm. About 30 g of theproduct were introduced into an aluminium pot. The weight of the pot andof the product were determined exactly. The pot with the sample of theproduct was then placed in a vacuum oven at a vacuum of 130 hPa at atemperature of 105° C. for 60 minutes. After drying, the pot was placedin a desiccator and allowed to cool for 30 minutes. The pot was thenweighed again. The weight loss was determined.

Residual solvent content in product P: The residual solvent content inthe product P was determined by head-space gas chromatography. 0.5±0.005g of the sample was weighed out and introduced into a head-space ampouleand a measured amount of solvent (1,2-dichlorobenzene, ODCB) was added.The ampoule was closed and shaken until the product had dissolved. Theampoule was heated until the volatile organic compounds had equilibratedbetween the sample and the gas phase in the ampoule (head-space). Partof the head-space gas was injected into a stream of carrier gas whichconveyed the sample along a chromatography column. Standards of knowncomposition were used for calibrating the GC. Toluene was added to thesolvent for use as internal standard.

Residual water content in the product P: The total amount of volatilecompounds is the sum of water, solvents and other volatile compounds.Since the proportion of other volatile compounds such as monomers wasusually less than 0.0005% by weight in the cases examined, the residualwater content could be determined by subtracting the solvent contentfrom the total content of volatile compounds.

The solvent content in the polymer-containing media PM was measured bymeans of gas chromatography. The internal standard was isooctane. Thesample was diluted with toluene and then injected into the gaschromatograph. The gas chromatography was carried out on an HP 6890chromatograph having the following specifications:

-   -   column type DB-5 from J&W, length 60 m, diameter 0.23 mm, film        thickness 1.0 μm    -   Injector temp.: 250° C.    -   Detector temp.: 350° C.    -   Carrier gas: helium    -   Column pressure: 96 kPa    -   Detector. FID

The following polymer-containing media PM were used for the examplesbelow:

Preparation of PM-I

A crude bromobutyl rubber solution was obtained from a commercialproduction plant and the organic phase was separated from the aqueousphase volume. The separation of the aqueous phase from the organic phaseis known from WO2010/031823 A, in particular FIG. 7 and the associateddescription. The organic phase was then used as PM-I for carrying outthe experiment. PM-I contained about 23% by weight of bromobutyl rubber,about 74% by weight of hexane isomers and 3% by weight of water,calculated on the basis of 100% by weight of these three components.(The concentration of the additives based on the bromobutyl rubberfraction was:

ESBO: from 1 to 1.6 phr, calcium stearate: from 1.3 to 1.7 phr andIrganox: from 0.03 to 0.1 phr

The bromobutyl rubber obtained from PM-I had the following propertiesafter extrusion:

Mooney (ML 1+8, 125° C.) from 28 to 36, content of bound bromine from1.6 to 2.0% by weight.

Example 1 Preconcentration

The Concentrator Unit

The concentrator unit used for the examples was similar to that depictedin WO2010/031823 A, in particular FIG. 1. A gear pump was used forpumping the polymer-containing medium PM-I which had been prepared asdescribed above to the heating device. The heating device was ashell-and-tube heat exchanger. A plurality of tubes which can be heatedinternally by means of steam are in this case accommodated in an outertube serving as the shell, which at the same time accommodates theproduct. In addition, mixing elements are provided on the outside of theinternal tubes which are in contact with the product in order to ensuregood heat transfer. The heating medium was steam, the flow of whichcould be regulated according to the temperature set for the medium. Apressure release valve was installed upstream of the concentrator unit,and the pressure upstream of the valve was controlled automatically to aset value. This set value was selected so that boiling of the heatedpolymer-containing medium PM-I in the heating device was prevented. Theheated polymer-containing medium PM-I was passed from the top into thedevolatilisation tank. The conical output of the devolatilisation tankwas equipped with a gear pump. The gear pump had the advantage that itwas able to handle high viscosities and build up high pressures. Sampleswere taken from the concentrated polymer-containing medium PM-II inorder to examine the concentration after the concentration stage.

Example 1

The heating medium of the heating device was set to 160° C., so that thepolymer-containing medium PM-I was heated to a temperature of 135° C.The pressure in the devolatilisation tank was atmospheric. For thepresent purposes, atmospheric pressure means that the vaporised volatileconstituents from the devolatilisation tank were conveyed through acondenser. The condenser was cooled by means of water and the condensedliquid constituents flowed into a collection vessel which was connecteddirectly to the environment. As a result, virtually ambient pressure wasestablished in the devolatilisation tank. The concentratedpolymer-containing medium PM-II at the output of the devolatilisationtank could be conveyed from the concentrator unit by means of theextraction pump as described above. The concentrated polymer-containingmedium PM-II had a hexane concentration of about 43% by weight.

The Devolatilisation Apparatus (1)

The preconcentrated PM-II was conveyed via a heating device into thedevolatilisation apparatus (1). The heating device was a heat exchangerof the same construction as was also used in the concentrator unit. Thedevolatilisation apparatus comprised a preextruder (2), a contrarotatingtwin-screw extruder having a hole diameter of D1=D2=57 mm and aneffective length of 720 mm, and a main extruder (3), a corotatingtwin-screw extruder having a hole diameter of D1=D2=58.3 mm and aneffective length of 3225 mm. Effective length in this case means thelength over which contact with the product takes place.

Both extruders of the devolatilisation apparatus comprised a regulatingvalve (5 or 5.1) as a pressure control device upstream of the respectivefeed zones (4 and 4.1) of the extruder or of the preextruder.

The preextruder had a devolatilisation zone (7.1) downstream of the feedzone (4.1) of the preextruder (6) and a devolatilisation zone (7.R)upstream of the feed zone (4.1) of the preextruder (6). Thedevolatilisation zone (7.R) had a devolatilisation opening (8.R) withdevolatilisation dome (9.R) which was connected to a gas discharge line,and the devolatilisation zone (7.1) had a devolatilisation opening (8.1)with devolatilisation dome (9.1) which was connected to a gas dischargeline. Downstream of the devolatilisation zone (7.1) of the preextruder(6) there was a pressure buildup zone (10.1) and a banking-up element(11). Downstream of the banking-up element (11), a transfer zone (12)led to the main extruder (3). The transfer zone (12) comprised aheatable tube which opened into the inlet of the regulating valve (5)which in turn marked the beginning of the feed zone (4) of the mainextruder (3).

The gas discharge lines of the preextruder (2) were connected to anextraction and condenser unit. The gases were extracted by means of avacuum pump from where the compressed gases were fed into a water-cooledcondenser. The barrel (13) of the preextruder was configured so as to beable to be heated by means of steam.

The main extruder had three devolatilisation zones (15.1, 15.2 and 15.3)located downstream of the feed zone (4) of the extruder (14) and onedevolatilisation zone (15.R) located upstream of the feed zone (4) ofthe extruder (14). The devolatilisation zone (15.R) had adevolatilisation opening (16.R) with devolatilisation dome (17.R) whichwas connected to a gas discharge line, and the devolatilisation zones(15.1, 15.2 and 15.3) each had a devolatilisation opening (16.1, 16.2and 16.3) with devolatilisation dome (17.1, 17.2 and 17.3) which was ineach case connected to a gas discharge line. The gas discharge lineswere connected to a condenser unit comprising a mechanical vacuum pumpand a downstream water-cooled condenser. The gas discharge lines wereconnected to a condenser unit comprising two mechanical vacuum pumpsconnected in series and a downstream water-cooled condenser.

Downstream of the devolatilisation zone (15.1) of the extruder (14)there was a pressure buildup zone (18.1) and downstream of this therewas a first dispersing zone (19.1).

Downstream of the devolatilisation zones (15.2 and 15.3) of the extruder(14) there was in each case likewise a pressure buildup zone (18.2 and18.3). Downstream of the pressure buildup zones (18.2 and 18.3) therewas in each case a dispersion zone (19.2 and 19.3). Between the pressurebuildup zones (18.1, 18.2 and 18.3) and the dispersion zones (19.1, 19.2and 19.3), there was in each case a banking-up element (20.1, 20.2 and20.3), and downstream of the dispersion zones (19.1 and 19.2) of theextruder (14) there was in each case a divided sieve disc pair (22.1 and22.2) removably fastened in the barrel (21).

Downstream of the last pressure buildup zone (18.3) of the extruder (14)there was the discharge zone (23) from the extruder. This discharge wasformed by a fixed die plate which opens into an underwater pelletizationdevice (24). Between the pressure buildup zone of the extruder (18.3)and the die plate of the pelletizer (23), there was a start-up valvewhich allows the product to be extruded via a bypass into a collectionvessel provided instead of the product being conveyed through the dieplate to the underwater pelletizer. This bypass is used, in particular,for starting-up and shutting-down the extrusion apparatus.

In the region of the dispersion zones (19.1, 19.2 and 19.3), theextruder had inlet openings (25.1, 25.2 and 25.3) for the introductionof stripping agents.

The barrel was made up of a plurality of parts and configured so that itcould be divided into three independently heated or cooled zones inorder to at least partially control the temperature profile in theextruder. Heating and cooling were effected by means of steam andcooling of water, respectively.

The treatment elements used for the devolatilisation, pressure buildupand dispersion zones and their specification are indicated in thefollowing examples.

Example 2

The preconcentrated polymer-containing medium PM-II obtained fromExample 1 was fed via a heating device into the devolatilisationapparatus at a rate of 180 kg/h, resulting in about 80 kg/h ofdevolatilised dry product at the discharge zone (24) of thedevolatilisation apparatus. The steam supply to the heating device wasset so that the temperature of PM-II at the regulating valve (5.1) wasabout 110° C. The pressure at the regulating valve was set to 1.3 MPa.The pressure in the two zones of the preextruder was set to 400 mbarabsolute. The heating temperature in the heatable parts of the barrel(13) of the preextruder was about 160° C. At the beginning of thetransfer zone (4), the rubber content of the further-concentratedpolymer-containing medium PM-II was about 80% by weight. PM-II was thenintroduced at a temperature of 100° C. and a pressure of about 2.0 MPainto the main extruder (3) in the feed zone (4). The pressure at thetransfer zone was obtained with the pressure control device at the feedzone of the main extruder completely opened.

Examples 3 to 6

The further-concentrated product PM-III obtained as described in Example1 and Example 2 was introduced into the main extruder (3) in whichdifferent screw elements were used in the devolatilisation zones anddispersing zones.

The devolatilisation zone (15.R) and the devolatilisation zone (15.1)were operated at an absolute pressure of about 100-180 mbar. Thepressure in the devolatilisation zones (15.2 and 15.3) was in each caseset to about 50 mbar absolute. From an engineering point of view, it isdifficult to keep a reduced pressure exactly constant in such a process,and there are therefore fluctuations which even out over the course ofthe experiment.

Nitrogen was introduced as stripping agent into the dispersing zone(19.1) downstream of the devolatilisation zone (15.1) at a rate of0.5-0.6 kg/h.

A dispersion composed of water and calcium stearate (45% by weight ofcalcium stearate) was introduced at a rate of 3.6 kg/h into thedispersing zone (19.2) downstream of the devolatilisation zone (15.2).

A dispersion composed of water and calcium stearate (45% by weight ofcalcium stearate) was introduced at a rate of 3.6 kg/h into thedispersing zone (19.3) downstream of the devolatilisation zone (15.3).

The speed of rotation of the extruder screws of the main extruder was inthe range from 60 min⁻ to 90 min⁻.

The screw elements used in the respective examples are summarised inTable 2a).

TABLE 2a Screw elements used Devolatilisation zones Dispersion zonesExample 15.1, 15.2 and 15.3 19.1, 19.2 and 19.3 3 two-flighted standardKneading blocks & eccentric discs Erdmenger profile analogous to FIG. 14 two-flighted standard Kneading blocks & eccentric discs Erdmengerprofile analogous to FIG. 1 5 two-flighted screw two-flighted screwelement with a element with a profile profile which can be continuallywhich can be differentiated analogous to FIG. 2b continuallydifferentiated analogous to FIG. 2b 6 two-flighted standard two-flightedstandard Erdmenger Erdmenger profile profile analogous to FIG. 3analogous to FIG. 1

TABLE 2b Pitch t and gap measurements Devolatilisation zones Example15.1, 15.2 and 15.3 3 R¹ _(max n) = R² _(max n) = 0.496 D_(n), t = 1.37D_(n) 4 R¹ _(max n) = R² _(max n) = 0.474 D_(n), t = 1.37 D_(n) 5 R¹_(max n) = R² _(max n) = 0.479 D_(n), t = 2.06 D_(n) 6 R¹ _(max n) = R²_(max n) = 0.474 D_(n), t = 2.06 D_(n)

TABLE 2c Results Hexane Total volatile content in the product Psubstances incl. water Example [ppm by weight] [% by weight] 3 (forcomparison) 2900 <0.30 4 (for comparison) 3000 <0.30 5 450 <0.30 6 500<0.30

The following can be seen from the examples:

In Example 3, none of the conditions S1), S2) or S3 is satisfied and thedevolatilisation result is unsatisfactory.

In Example 4, only the condition S1) is satisfied and thedevolatilisation result is unsatisfactory.

In Example 5, all conditions S1), S2) and S3) are satisfied and thedevolatilisation result is very good.

In Example 6, the conditions S1) and S2) are satisfied and thedevolatilising result is likewise very good.

What is claimed is:
 1. A devolatilisation apparatus comprising at leastone extruder, the extruder comprising: a barrel and n barrel holes B_(n)having associated hole diameters D_(n) where n is an integer, one ormore screws W_(n) arranged concentrically in each of the barrel holesB_(n) and configured to be rotatable within the barrel holes, whereineach screw has an axis of rotation A_(n) and is equipped with treatmentelements, the treatment elements having a cross-sectional profileorthogonal to the axis of rotation, wherein the cross-sectional profilein a circumferential direction has: m relative maxima R^(m) _(max n) inrespect of a radial dimension of the cross-sectional profile to the axisof rotation A_(n) of the screw W_(n), where m is an integer from 1 to 8,a maximum value R_(max n) in respect of radial dimension of thecross-sectional profile to the axis of rotation A_(n) of the screwW_(n), where R_(max n) fulfils:R_(max n)<=(D _(n)/2) at least one feed zone, one or moredevolatilisation zones comprising in each case at least onedevolatilisation opening which is suitable for discharge of volatileconstituents from a polymer-containing medium from the extruder, atleast one discharge zone, and wherein the treatment elements comprisescrew elements having a pitch t, and the screw element are configured sothat each of the following three conditions are met: S1) thecross-sectional profile has at least one relative maximum R^(m) _(max n)based on the radial dimension of the profile curve, for which:0.420 D_(n)<R^(m) _(max n)<0.490 D_(n), S2) 1.38 D_(n)<t<5.00 D_(n), andS3) the cross-sectional profile of the respective screw element has notangential angle β greater than 30°, on the active flanks located at thefront in the direction of rotation in the range of the radial dimensionfrom 0.95 R_(max) to R_(max), where the tangential angle β is defined asa smaller of the two angles formed on drawing tangents at any point onthe cross-sectional profile of the treatment element at which thecross-sectional profile cannot be continually differentiated, and is 0°at any point on the cross-sectional profile of the treatment element atwhich the cross-sectional profile can always be differentiated.
 2. Thedevolatilisation apparatus according to claim 1, wherein: the extrudercomprises at least one of a single-screw extruder and a multiscrewextruder; and the screw elements SE have a modular construction andcomprise a core shaft and screw elements which have an accommodationopening for the core shafts or are configured as screws having a solidconstruction or as screws comprising individual subsegments and producedin solid construction.
 3. The devolatilisation apparatus according toclaim 1, wherein n=2 to 8, and the barrel holes pass through oppositeone another and are arranged parallel to one another.
 4. Thedevolatilisation apparatus according to claim 1, wherein n=2, and thebarrel holes B_(n) pass through and are arranged parallel to oneanother.
 5. The devolatilisation apparatus according to claim 1,wherein: for R^(m) _(max n), m is 2, for S1), 0.450 D_(n)<R^(m)_(max n)<0.480 D_(n), for S2), 1.90 D_(n)<t<2.40 D_(n), and for S3), thecross-sectional profile of the respective screw element has notangential angle β greater than 10° on the active flanks located at thefront in the direction of rotation in the entire range of the radialdimension from 0 to R_(max).
 6. The devolatilisation apparatus accordingto claim 1, wherein: the extruder has at least one dispersing zone; andthe devolatilisation apparatus comprises 1 to 20 devolatilisation zones,the devolatilisation zones, in the transport direction of the extruder,define a last devolatilisation zone, and at least the lastdevolatilisation zone is equipped with screw elements SE.
 7. Thedevolatilisation apparatus according to claim 6, wherein thedevolatilisation apparatus comprises 2 to 8 devolatilisation zones, atleast one devolatilisation zone is located upstream of the teed zone ofthe extruder, and ail of the devolatilization zones are equipped withscrew elements SE.
 8. The devolatilisation apparatus according to claim1, wherein the devolatilisation openings comprise devolatilisationdomes, and the devolatilisation openings and devolatilisation domes areconfigured for preventing or reducing exit of polymer-containing mediumtherethrough.
 9. The devolatilisation apparatus according to claim 1,wherein surfaces within the devolatilisation openings comprise coatingswhich reduce or prevent adhesion of material being devolatilised to thesurface.
 10. The devolatilisation apparatus according to claim 1,wherein the extruder comprises: one or more feed openings for theintroduction of additives; and at least one depressurisation elementlocated upstream of at least some of the devolatilisation zones of theextruder.
 11. The devolatilisation apparatus according to claim 10,wherein the depressurisation elements comprise perforated plates, andthe perforated plates are made up of a plurality of parts so that theycan be taken from the barrel without removal of the screws from thebarrel.
 12. The devolatilisation apparatus according to claim 1,wherein; the screw elements SE are two-flighted or three-flighted; andthe screw elements SE have a cross-sectional profile representedcompletely by a profile curve which can he continually differentiated.13. The devolatilisation apparatus according to claim 12, wherein thescrew elements SE are unsymmetrical or symmetrical.
 14. Thedevolatilisation apparatus according to claim 1, wherein the screwelements SE have a longitudinal axis M*, a core radius Rj and an outerradius R_(a) in which each have the longitudinal axis M* as midpoint, anouter contour A(φ)running around the longitudinal axis M*, where φ isthe angle around the longitudinal axis M*, and R_(j)<D_(A)((P)<R_(a)fora spacing D_(A)((p) of the outer contour A (φ) from the longitudinalaxis M, and further wherein the outer contour A(φ) has at least oneouter contour section A(Δφ) which runs along an angular section Δφ andhas a continually changing spacing D_(A)(Δφ) from the longitudinal axisM*, where Rj<D_(A)(Δφ)<R_(a), and has an associated evolute E, which isa number of n points P(i) where i=1 to n and n>3, where each of thepoints P(i) is located outside the longitudinal axis M* and within theouter radius R_(a), and each two adjacent points P(i)and P(i+1) have aspacing Δr(i) from one another which is less than R_(j)/2.
 15. Thedevolatilisation apparatus according to claim 1, wherein the screwelements SE are made of steel or powder-metallurgically producedmetallic composites based on iron, nickel or cobalt.
 16. Thedevolatilisation apparatus according to claim 1, further comprising; oneor more concentrator units located upstream of the extruder; and adevolatilisation extruder or devolatilisation kneader located upstreamof the extruder.
 17. The devolatilisation apparatus according to claim16, further comprising a transfer zone connecting the devolatilisingpreextruder or devolatilising prekneader and the extruder, wherein thetransfer zone has at east one depressurisation element.
 18. Thedevolatilisation apparatus according to claim 17, wherein the transferzone has one depressurisation element and further comprises at least onepressure regulating unit.